Watson Wyatt and Towers Perrin executives are excited about their deal to create Towers Watson, but investors are not cheering as much. 

Watson Wyatt’s shares plunged nearly 10 percent in Monday morning trading, as investors woke up to the all-stock deal valued at about $3.5 billion, announced Sunday.

A Citi analyst downgraded the Watson Wyatt, which is publicly held, to “hold” from “buy”, calling the companies’ three-year integration plan a “major risk.” 

Among the concerns: integration and deal costs may lower earnings, and rivals like Hewitt and Mercer could grab people and other opportunities in the interim. 

It will take three years to achieve savings of $80 million through job cuts and the streamlining of overlapping operations. The companies also expect one-time costs of $80 million from the merger and “significant noncash expenses” for the first two years.